Method for manufacturing stent-grafts

ABSTRACT

A sewing machine is provided which is capable of sewing reinforcing wire to tubular grafts in order to form stent grafts. A bobbin (which may be seated in a shuttle) carries a bottom thread through the bore of the tubular graft and forms a stitch in combination with a top thread carried on a needle which pierces the graft wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/476,349 filed Sep. 10, 2004, now U.S. Pat. No. 7,073,456 which is anational stage filing under 35 USC §371 of PCT/GB02/01970 (filed May 1,2002), both of which are incorporated by reference herein.

FIELD OF THE INVENTION

This application relates to a sewing machine and in particular to asewing machine for use in the construction of vascular stent-grafts.

BACKGROUND OF THE INVENTION

Stent-grafts are tubular constructions for use inside blood vessels.They generally comprise two components: a quasi blood-tight tube that isusually formed of textile or membranous material, and a reinforcingstructure which is usually made of wire or other filamentous metallicmaterial.

The tubular graft component is usually made from woven polyester fabric,although a few designs employ PTFE membranes. The graft is supported onmetallic rings which are generally formed from wire but are occasionallycut from metal tube by means of laser cutting or similar means. Whenattached to the graft, the metal rings can define a single plane at anangle to the axis of the graft, the rings can be corrugated so that theydefine the surface of a short cylinder on the surface of the graft, orthe rings can be fenestrated or linked so as to produce a longcylindrical reinforcing element on the surface of the graft.

In almost all designs, the reinforcing rings are attached to the surfaceof the graft by means of sutures which are generally applied by hand.Some designs employ many hundreds or thousands of sutures and the timeand cost associated with attaching these sutures is high. Additionally,the burden of assuring the quality of every stitch is expensive, whilethe implications of poor quality stitching in a device which isimplanted into a patient can be particularly serious to the health ofthe patient.

There is also a requirement to manufacture stent-grafts to fit theanatomies of individual patients. In particular, the lengths, diameters,tapers, secondary tapers and the location of side-branches ofstent-grafts are required to be tailor-made for each patient and thiscan take an unfeasible period of time when the stent-graft is made byhand.

An alternative solution has been described in WO 99/37242 (in the nameof the present applicant) in which computerised embroidery is used tomanufacture a flat-form device which is subsequently rolled into a tube.This approach solves many of the issues associated with handmanufacturing but results in a seam and prevent some continuousstructures from being designed.

GB 2165559 (University College London) discloses a sewing machine forforming stitches in a substrate, for example body tissue, duringsurgery. The sewing machine employs suction to pull a folded section ofthe substrate into the machine so that it is disposed between a needleand a hook. The needle can then be used to feed thread through thefolded section of substrate to emerge the other side, and to engage thethread on the hook. This action is repeated with the sewing machinebeing moved along the substrate, thereby forming stitches in thesubstrate. This sewing machine could not be employed to stitch thread tothe wall of a tubular graft, because the graft would not be sufficientlycompliant to enable a folded section of graft to be sucked into themachine.

U.S. Pat. No. 4,502,159 (Shiley Incorporated) discloses a method forforming a tubular prosthesis by rolling pericardial tissue into a tubeand stitching along the tube to form a longitudinal seam. However, thestitches are formed conventionally by passing a thread from one side ofthe seam to the other on the outside of the tube.

U.S. Pat. No. 4,241,681 (Porter) discloses a sewing machine for sewing aseries of spaced reinforcing rings on a long flexible tube of fireprooffabric. The machine comprises, a long tubular support over which thework piece is pulled like a sleeve on an arm. A fixed stitchingmechanism is provided for forming chain stitch in the work piece, and apuller mechanism advances the work piece over the support as thestitches are formed therein.

U.S. Pat. No. 4,414,908 (Janome Sewing Machine Co., Limited) discloses asuturing machine for suturing incised parts of a patient. The machinecomprises a needle holder (effectively a pair of pliers) and a shuttleholder which is slideably mounted on the needle holder. This means thatmovement of the needle independently of the shuttle is not possible forall degrees of freedom. In particular, movement of the needle holder topierce the needle through the wall of a tubular implant would inevitablyresult in a corresponding movement of the shuttle within the bore of theimplant. In practice, it would not be possible to manipulate the needlewithout causing the shuttle to impact the side walls of the implant,thereby risking damage to the implant.

In an alternative embodiment of U.S. Pat. No. 4,414,908, the shuttle ismounted on a rod which is slideable parallel to the longitudinal axis ofthe needle holder and the needle holder is rotatable circumferentiallyabout the axis of the shuttle rod. This means that rotation of theneedle holder causes the needle to follow a circumferential path whichis a constant distance from the shuttle. Thus the needle could neverpenetrate the side wall of a tubular implant. Rather, it would simplycircle around the implant, keeping a constant distance from the centreof the bore.

SUMMARY OF THE INVENTION

The present invention is designed to address the above-mentionedshort-comings by allowing the reinforcing rings to be attached bysutures which are applied with a sewing machine which is controlled bycomputer. The sewing machine comprises a number of novel mechanismswhich permit sewing onto the surface of narrow tubes and the stitchingof wires or other structures onto the surface of the tube. Specifically,structures can be sewn to the inner or outer surfaces of the tube.

The machine described herein can also be used to manufacture othertubular devices which incorporate a filamentous component in which thefilamentous component is applied to the surface of the tube in aseparate operation to the formation of the tube itself.

WO 01/30269 (in the name of the present applicant) was published afterthe priority date of the present application. It relates to a method andapparatus for stitching thread to the wall of a graft, for example toform a graft-stent. The present invention is an improvement thereto.

According to a first aspect of the present invention, there is providedapparatus for stitching thread to the wall of a tubular medical implant,comprising a support for the implant, a needle to drive a first threadthrough the wall and into the bore of the implant, and a bobbin forcarrying a second thread through an open end of the implant into saidbore in order to form a stitch in combination with the first thread.

The needle and the bobbin are preferably disposed so that thelongitudinal axes thereof lie in a common plane. Preferably, the axesare at 90.degree.

The relative positioning of the needle and the bobbin allows thestitches to be made in a more confined environment than is possible witha conventional sewing machine, thereby allowing stitches to be made inthe wall of relatively small diameter tubular grafts.

According to a second aspect of the present invention, there is providedapparatus for stitching thread to the wall of a tubular medical implant,comprising a support for the implant, a needle to drive a first threadthrough the wall and into the bore of the implant, and a bobbin forcarrying a second thread through an open end of the implant into saidbore in order to form a stitch in combination with the first thread,wherein an elongate bobbin support is provided to support the bobbininside the bore of the implant.

In a preferred embodiment, the bobbin support is a rod having a recessin which the bobbin can be seated.

In an alternative embodiment, the bobbin support is a runner in whichthe bobbin is free to move into and out of said bore. Preferably, therunner is in the form of a tube with a slot provided therein to allowthe needle access to the bobbin through the slot.

In a particularly preferred embodiment, the bobbin sits in a shuttlewhich itself either sits in the recess in the rod or is able to move upand down the runner.

Preferably, the shuttle is biased towards the side of the runnerproximate the path of the needle so that in use the shuttle ispositioned to engage the loop of the first thread, the biasing beingsuch as to allow movement of the shuttle away from the bias to asufficient extent to allow the second thread to be wound on and off theshuttle.

In a further embodiment, at least one end of the shuttle is narrowed andoptionally curved so that when its orientation is maintained in therunner as described above, the tip of the shuttle is brought close tothe tip of the needle and the centre of the loop of suture.

The embodiment in which the bobbin sits in a runner is particularlysuitable for small diameter grafts (perhaps from 3 to 6 mm), whereas theembodiment in which the bobbin is seated in a recess in a rod issuitable for grafts having a larger diameter (perhaps from 7 to 40 mm).

In a preferred embodiment, friction is applied to the second thread byweaving it through a series of holes in the shuttle or bobbin carrier,the greater the number of holes, the greater the braking effect.

In one embodiment, said apparatus additionally comprises means fortensioning said second thread to facilitate the formation of stitches.The means for tensioning may comprise a trapping body adapted to movealong the runner independently of the shuttle and a stop on the oppositeside of the shuttle to the trapping body, the arrangement being suchthat in use the second thread passes between the trapping body and theshuttle as it leaves the shuttle and can be trapped between the trappingbody and the shuttle by urging the trapping body into the shuttleagainst the stop, in order to allow tension to be applied to the secondthread when forming a stitch.

In an alternative embodiment, the means for tensioning the second threadcomprises resilient metal (such as a leaf spring) to trap the thread.The apparatus may comprise means for applying additional pressure to theresilient metal in order to facilitate the tensioning of the thread;said means may have the additional function of moving the shuttle alongthe runner. Thus the travel of the shuttle can be practically achievedby means of push rods which act on it at either end of the guide tube.

In a further embodiment, the apparatus may comprise a variable brake onthe bobbin in the form of a screw acting on the bobbin, preferably viaan ‘O’ ring rubber washer.

A yet further embodiment comprises a shuttle or bobbin carrier which canbe rolled in order that the second thread has lie to across the surfacethereof to increase the friction acting on the second thread and therebyhave a braking effect.

In one embodiment, the manufacturing machine here described forms a twothreaded lock stitch by means of a bobbin-carrier (and the mechanism)which is able to pass through the lumen of the tube being manufactured.During manufacture, a guiding tube passes through the entire length ofthe stent-graft and projects at either end of it. The guiding tubepossesses a slit (which may be along its entire length) through whichthe needle passes to gain access to the shuttle. The needle carries, atits tip, a loop of suture material (or any thread), both free ends ofwhich remain on the outer surface of the stent-graft. Ideally, the guidetube has a non-circular cross section so as to provide rigidity whichhas been lost as a result of forming the longitudinal slit.

The guide tube may be formed from at least one shaped strip of materialwhich retains the shuttle by gravitational, magnetic or other nearconstant-force action. A second strip of material may form the tube inconjunction with the first.

According to a third aspect of the present invention, there is providedapparatus for stitching thread to the wall of a tubular medical implant,comprising a support for the implant, a needle to drive a first threadthrough the wall and into the bore of the implant, and a bobbin forcarrying a second thread through an open end of the implant into saidbore in order to form a stitch in combination with the first thread, thebobbin being mounted in a shuttle, wherein the shuttle is an elongateelement with a D-shaped cross section for at least part of its length.

Preferably, the needle passes between the implant wall and thesubstantially planar longitudinal surface of the shuttle.

The shuttle preferably comprises a bobbin within a bobbin-carrier whichis shaped approximately like a long, narrow cylinder. Ideally, thebobbin-carrier is not quite circular in cross section but has a feature,preferably a flattened surface, which can register against acorresponding feature in the guide tube, thereby maintaining theorientation of the bobbin-carrier about its long axis.

The needle is preferably shaped so as to be substantially straight witha section removed (a “scarf”) to facilitate the formation of a loop.There may be a corresponding section “removed” from the shuttle in orderthat the needle and the shuttle fit together to enable them to occupyless room inside the bore of the graft than in a conventional sewingmachine.

An unusual requirement when sewing stent-grafts is that structuresshould be able to be attached to each other only with the strength of astitch. This is achieved in the current machine by independent controlof the tension of threads in the bobbin and needle. Control of thebobbin thread has been described above and control of the needle threadis achieved by means of an electronically controlled tensioner whichoperates independently of the position of the needle.

According to a fourth aspect of the present invention, there is providedapparatus for stitching thread to the wall of a tubular medical implant,comprising a support for the implant, a needle to drive a first threadthrough the wall and into the bore of the implant, and a bobbin forcarrying a second thread through an open end of the implant into saidbore in order to form a stitch in combination with the first thread, andmeans for tensioning the first thread, wherein the means for tensioningoperates independently of the mechanism for driving the needle.

A strain gauge may be provided in the path of the first thread, thesecond thread or both.

The stent-graft manufacturing machine requires a mechanism to hold thetubular stent-graft while reinforcements are stitched to its surface.Stent-grafts can have cylindrical sections and conical sections in themand along the length of an implant the rate of change of the diameter ofthe implant can have a number of different values. Stent-grafts may alsobe branched.

In order that the surface of the stent-graft is presented to the sewinghead in a constant fashion, the machine incorporates a pair ofattachment means which grip the stent-graft at its either ends in a waythat allows the graft to be tensioned along its axis, to be translatedalong its axis and to be rotated about its axis. Additionally, the graftand attachment means can be rotated about a point or points on thesurface of the graft so that the wall of the graft being stitched isretained at a constant distance and/or angle from the sewing head.

According to a fifth aspect of the present invention, there is provideda method for stitching thread to the wall of a tubular medical implant,comprising the steps of driving a first thread through the wall and intothe bore of the implant using a needle, forming a loop of the firstthread, moving a bobbin carrying a second thread through an open end ofthe implant into said bore, passing the second thread through the loopformed in the first thread, closing said loop in order to form a stitch,and withdrawing the bobbin from said bore.

In a preferred embodiment, the needle and the bobbin are disposed sothat the longitudinal axes thereof lie in a common plane, and the needleis withdrawn sufficiently (preferably entirely) before the second threadis passed through the loop formed in the first thread in order that thebobbin does not contact the needle.

In a particularly preferred embodiment the following novel sequence ofmovements of the bobbin-carrier and needle are employed:

The needle passes through the wall of the stent-graft and approaches theopposite wall of the guide tube within the stent-graft.

The needle is partially withdrawn.

The shuttle is advanced until the tip of its nose engages the loop ofsuture.

The shuttle can be stopped at this point.

The needle is withdrawn further and can be pulled through the wall ofthe stent-graft.

The shuttle is advanced through the loop of suture. If insufficientthread is present, the shape of the nose of the shuttle will draw moreneedle thread through the wall of the stent-graft and into the guidetube to permit the shuttle to pass completely through the loop.

In a sixth aspect of the present invention, therefore, there is provideda method for stitching thread to the wall of a tubular medical implant,comprising the steps of driving a first thread through the wall and intothe bore of the implant using a needle, forming a loop of the firstthread, moving a bobbin carrying a second thread through the loop formedin the first thread, closing said loop in order to form a stitch,wherein said loop is formed in the first thread by beginning to withdrawthe needle, but wherein the end of the needle is withdrawn completelyfrom the bore only after the shuttle has engaged said loop.

The advantage of this method is that the sequential deployment of thebobbin and the needle enables the thread formation to take place in arestricted volume compared to prior art methods (which require that theneedle and bobbin are adjacent simultaneously).

The first thread may be clamped whilst the stitch is being formed inorder to create sufficient tension to unwind the second thread from theshuttle.

The mechanism driving the needle is also novel and is able to controlthe position of the needle at any instant to allow control of the needleindependent of the bobbin. Conventional sewing machines employ a cammechanism which links the movement of the bobbin to that of the needleand requires that the movements of each component be smooth andcontinuous. As described in the above sequence, the needle and bobbin ofthe present invention are controllable independently and continuousmovement is not a requirement.

In a seventh aspect of the present invention, there is provided a methodfor stitching thread to the wall of a tubular medical implant having astraight section with substantially parallel walls and at least onetapered section with tapered walls, comprising the steps of driving afirst thread through the wall and into the bore of the implant using aneedle, forming a loop of the first thread, moving a bobbin carrying asecond thread through an open end of the implant into said bore andpassing the second thread through the loop formed in the first thread,closing said loop in order to form a stitch, and withdrawing the bobbinfrom said bore, wherein the implant is tilted in order that the axisalong which the bobbin travels is substantially parallel to the wall inwhich the stitch is to be formed.

In order to aid the placement of features onto the surface of theimplant a number of wire or reinforcement handling features can beadded:

According to an eighth aspect of the present invention, there isprovided a method for attaching reinforcement wire to the surface of amedical implant, comprising the steps of determining the position atwhich the wire is to be attached, locating the wire proximate saidposition, employing a needle to move the wire closer to said position,and employing said needle to make a stitch in the surface.

The needle is preferably positioned on the side of the wire opposite tothe position at which the wire is to be attached with the tip of theneedle disposed between the plane of the surface and the plane of thetangent of the wire parallel to the plane of the surface, moved towardssaid position such that it contacts the wire and moves it closer to saidposition, and moved substantially perpendicular to the surface to make astitch therein.

The method steps are then repeated and the needle is employed in thesecond cycle to move the wire closer to the stitch formed in the firstcycle, the thread passing over the wire from the first to the secondstitch thereby attaching the wire to the surface close to or at the saidposition.

The apparatus preferably comprises means for determining the level ofthe graft surface and controlling the height of the needle relative tosaid level. This may simply be open loop control software whichreferences the graft surface, although means for sensing the surface ofthe graft may be provided, with feedback software being provided tocontrol the height of the needle.

This allows precise positioning of the wire on the surface of, forexample, the tubular graft, the positioning step being incorporated intothe sewing steps so result in an efficient and speedy process. It alsorestores the wire to its true shape, avoids the need for sensing exactlywhere the wire is, and avoids the situation in which the needle strikesthe wire and is damaged.

In a preferred embodiment, the method includes the step of deforming thewire in order to attach wire in a pre-determined configuration to thegraft without the need for having pre-formed the wire into thatconfiguration.

According to a ninth aspect of the present invention, there is providedapparatus for attaching reinforcing (or other) filament to a tubularmedical implant, comprising a support for the implant, a needle to drivea first thread through the wall and into the bore of the implant, and ashuttle for carrying a second thread through an open end of the implantinto said bore in order to form a stitch in combination with the firstthread to attach the reinforcing filament to the implant wall, whereinthe apparatus additionally comprises a support (such as a table) for thereinforcing filament, the support being moveable relative to the implantto enable the reinforcing filament to be positioned on the implant(preferably under tension) prior to attachment to the implant.

In one embodiment of a stent-graft, the wire reinforcing rings areformed from a continuous piece of wire which is formed into a flat,zig-zag pattern. In order to apply the wire to the stent-graft it isheld on a moving tray which contains a belt feed mechanism. The feederpushes the wire zig-zag down the tray to correspond with the wire being,attached along the length of the implant. The tray translates from sideto side to allow the wire to be fed around the circumference of thestent-graft. By means of this mechanism, a stent-graft can be assembledautomatically from the component parts of a graft tube and a pre-formedwire reinforcement.

According to an tenth aspect of the present invention, there is providedapparatus for shaping a length of reinforcing wire formed from a shapememory alloy prior to attachment of the wire to a medical implant,comprising means for holding and dispensing the wire, and means forlaying the wire in the required pattern on the implant, wherein theapparatus additionally comprises means for localised heating of the wirein order to fix the wire into the required pattern prior to attachmentto the implant.

An improvement on the above system which allows a wider range ofstent-grafts to be manufactured automatically includes a mechanism tomake the appropriate bends in wire just prior to its attachment to thesurface of the stent-graft. Such a mechanism comprises a spool of wireand feed mechanism and at least one pair of jaws which incorporate thedesired radius of bend or can be used together to form the desiredradius of bend. When the jaws grasp the wire and heat is applied, thewire will adopt a ‘set’ as defined by the radius of curvature of thejaws or the way in which the pairs of jaws are positioned with respectto one another. Conveniently, heat can be applied by passing anelectrical current through the wire or by heating the jaws directly,although other means are well known. Ideally, the jaws can be made of anengineering ceramic material which will have the strength to form thewire and resist heat but the insulating properties required to be ableto pass an electric current through the wire.

Some other structures which are applied to the surface of stent-graftsalso require forming but do not require heat or high forces to achievethe necessary ‘set’. An example of such a structure is a radio-opaquemarker which can be made of a metal with a high atomic number or from apolymer which incorporates metals or salts with a similar atomic number.One suitable metal is tantalum, which is highly malleable.

In a eleventh aspect of the present invention, therefore, there isprovided apparatus for attaching wire (preferably a marker wire) to thewall of a tubular medical implant circumferentially around the implantand longitudinally along the implant, comprising a support for theimplant, a needle to drive a first thread through the wall and into thebore of the implant, a bobbin for carrying a second thread through anopen end of the implant into said bore in order to form a stitch incombination with the first thread to attach the wire to the implantwall, and a tube through which the wire is fed in order to be placed onthe implant in the correct position prior to attachment to the implant,wherein the said tube is adapted to move from a first position in whichit is perpendicular to the longitudinal axis of the implant to a secondposition in which it is parallel to said axis, to facilitate positioningof the wire on the implant. Preferably, the tube can be positioned tofeed wire adjacent to the needle from any direction around the axis ofthe needle. Pinch rollers may be provided to feed said wire down saidtube.

The machine described advantageously incorporates a spool of tantalumwire or similar filamentous material of appropriate radio-opacity and aguiding orifice or tube. The orientation of the guiding orifice or tubeis controlled by computer so that depending upon the movement of thestent-graft (i.e. whether rotating or translating about its axis) thefilamentous material can be fed out under the sewing head along the lineof movement of the surface of the stent-graft. As a result of themalleable nature of the filamentous material, it can be so arranged tolie circumferentially about the stent-graft or in parallel with itsaxis.

With improvement, the mechanism can be adapted to wrap wires spirallyalong the body of the stent-graft and this can permit other designs ofreinforcement means to be attached or for other patterns of filamentousstructure to be attached to the surface of the implant.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of preferred embodiments of the present invention will now bedescribed with reference to the accompanying drawings, in which:

FIG. 1 is a schematic depiction, in perspective, of apparatus inaccordance with the invention;

FIG. 2 is a side view in partial cross-section of a shuttle inaccordance with the invention;

FIG. 3 is an end view in partial cross-section of an alternativeembodiment of the shuttle of FIG. 2 in the guide tube of FIG. 1;

FIG. 4A is a perspective view of an alternative embodiment of a shuttlein accordance with the invention;

FIG. 4B is a perspective view of a shuttle support in accordance withthe invention; and

FIG. 4C is a perspective view of the shuttle of FIG. 4A seated in theshuttle support of FIG. 4B.

FIGS. 5A to 5D depict schematically the operation of the apparatus inaccordance with the invention to attach wire to the surface of a graft.

DETAILED DESCRIPTION OF PREFERRED VERSIONS OF THE INVENTION

Turning to FIG. 1, sewing machine 1 comprises a base 2 having mountedthereon a sew arm 10, shuttle tube 20 and stent table 30.

Graft 5 is held by a pair of grips (not shown) at either end of graft 5with shuttle tube 20 passing through the lumen of graft 5 and beingsupported at either end by shuttle tube supports 25 which are alsomounted on base 2.

Sew arm 10 is mounted on carriage 3 which is driven by carriage drive 4in directions parallel and perpendicular to shuttle tube 20 (asindicated by arrows A and B respectively) so that sew arm 10 can bepositioned as required relative to graft 5.

Sew arm 10 comprises a needle head 11 which projects over the edge ofcarriage 3 and which has needle 12 which can be driven up and downrelative to graft 5 (as indicated by arrow C) and side to side(so-called “needle wobble”) by needle wobble drive (as indicated byarrow D). Needle head 11 controls the deployment of the top thread (notshown), which passes from a spool (not shown) to stitch maker 15(controlled by stitch maker motor 16), though the eye of needle 12 andthen engages with top thread tensioner 14.

The wire which is used to form the stent on the surface of graft 5 islaid pre-formed on stent table 30, which is driven into positionrelative to graft 5 by stent table drive 31 in the direction shown byarrow E. The wire (not shown) is retained in position whilst being sewnto graft 5 by wire guide 32 which is attached to sew arm 10.

Turning to FIGS. 2 and 3, shuttle 40 comprises a bobbin 41 for carryingthe bottom thread (not shown) and a bobbin carrier 44 for bobbin 41.Bobbin 41 is in the form of an elongate spool with a narrowed centralaxis 42 around which the bottom thread can be wound and end rollers 43about which bobbin 41 can roll so that the thread can unwind from axis42. Bobbin 41 sits loosely in the central cavity of bobbin carrier 44 toenable thread to be unspooled easily from bobbin 41.

Bobbin carrier 44 is elongate in shape and has asymmetric nose 45 whichis displaced laterally from the longitudinal axis of bobbin carrier 44so as to engage a loop of top thread as will be described below. Thebody of bobbin carrier 44 (that part distinct from nose 45) has paralleltop and bottom walls connected by a flat side wall 46 and a curved sidewall opposite to side wall 46. This shape mirrors the shape of theinternal cavity of shuttle tube 20, so that shuttle 40 can be seatedloosely in shuttle tube 20 with flat side wall 46 substantially parallelto flat side wall 22 of shuttle tube 20. In this manner, shuttle 40 canbe moved longitudinally back and forth along shuttle tube 20 but isprevented from rotating about its longitudinal axis because side wall 46is longer than the notional internal diameter of the curved section ofshuttle tube 20.

It will be noted that FIGS. 2 and 3 depict slightly differentembodiments, in that the external profile of bobbin carrier 44 differssomewhat. However, the function is unaltered, and in particular wall 46acts in both cases to prevent bobbin carrier 44 from rotating in shuttletube 20.

FIG. 3 also depicts slot 21 in shuttle tube 20, through which needle 12passes during the sewing process (described below).

FIG. 4A depicts an alternative embodiment of a shuttle 50 comprisingbobbin 41 with central axis 42 and end rollers 43 as described above,and bobbin carrier 51 which is formed substantially similarly to bobbincarrier 44 described above except that the nose 52 of bobbin carrier 51is symmetrical in shape about the vertical plane containing itslongitudinal axis.

FIG. 4C shows shuttle 50 seated in recess 54 of shuttle rod 53, which isshown on its own in FIG. 4B. Shuttle rod 53 also has slit 55 therein,disposed in a vertical plane containing its longitudinal axis.

Returning to FIG. 1, shuttle drive motor 26 operates to drive shuttledrive arms 23 into and out of either end of shuttle tube 20 in thedirection of arrow F so as to move shuttle 40 backwards and forwardsalong shuttle tube 20.

Shuttle thread tensioner 24 operates to tension the bottom thread onbobbin 41 by increasing the pressure on a leaf spring 47 so as to trapthe bottom thread under leaf spring 47, thereby enabling tension to beapplied.

The position of graft 5 relative to shuttle tube 20 can be adjusted bymeans of graft bed height drive 6, which moves graft bed 7 (on whichgraft 5 rests) up and down relative to shuttle tube 20 (in the directionof arrow G) and from side to side parallel to the longitudinal axis ofshuttle tube 20 (in the direction of arrow H).

If it is necessary to tilt graft 5 (for example when sewing on thesurface of a tapered position) then this can be done by means of grafttilt drive 8, which raises and lowers one end of graft 5 in thedirection shown by arrow I. Graft 5 is rotated about its longitudinalaxis (in the direction of arrow J) by rotation of the graft grip ateither end.

The operation of sewing machine 1 will now be described with referenceto FIGS. 1 to 3.

Graft 5 is placed over shuttle tube 20 by disengaging shuttle tube 20from shuttle tube support 25 and passing graft 5 over shuttle tube 20 sothat shuttle tube 20 passes through the lumen of graft 5. The graftgrips (not shown) are then operated to engage either end of graft 5 andgraft 5 is positioned correctly with respect to needle head 11 byoperation of graft bed height drive 6 and graft tilt drive 8. Rotationof graft 5 about its longitudinal axis takes place to ensure that thesurface of graft 5 to which a support wire is to be sewn is facingupwards away from base 2.

The support wire for forming the stent on graft 5 is pre-formed on stenttable 30, which is positioned over the surface of graft 5 by operatingstent table drive 31. The support wire is held in place over graft 5 bywire guide 32 on sew arm 10, which is in turn driven into place overgraft 5 by operation of carriage drive 4 to drive carriage 3.

The above process locates the support wire approximately into positionwith respect to graft 5. The support wire may be accurately positionedby operating needle wobble drive as will be described below withreference to FIGS. 5A to 5D:

Needle 12, which carries the top thread 61, is first positioned close tosupport wire 60 and then lowered (arrow C) to be just above the surfaceof graft 5. Needle 12 is then moved sideways (arrow D) by needle wobbledrive to push wire 60 close to the previous stitch. Needle 12 is thendriven downwardly through the wall of graft 5 at position 62 close towire 60.

Once needle 12 has fully pierced the wall of graft 5 it passes throughslot 21 in shuttle tube 20 so that the end of needle 12 is positionedtowards the end of side wall distal from slot 21. Needle 12 is thenpartially withdrawn so that the friction between the top thread and thewall of graft 5 causes the creation of a loop in the top thread withinshuttle tube 20.

Shuttle drive motor 26 now operates on shuttle drive arm 23 to driveshuttle 40 down shuttle tube 20 into the lumen of graft 5 withasymmetric nose 45 of bobbin carrier 44 in front. As shuttle 40 isadvanced towards the loop of top thread, nose 45 engages the loop, aidedby the asymmetric positioning of nose 45 towards flat side wall 46 ofbobbin carrier 44. The bottom thread, which is wound around central axis42 of bobbin 41, trails behind shuttle 40.

Once shuttle 40 has engaged the loop of top thread its movement ishalted and needle 12 is withdrawn completely from the wall of graft 5,leaving behind a loop of the top thread. Shuttle 40 is then advanced sothat it passes completely through the loop of top thread and emerges onthe other side.

A stitch is now formed by passing the bottom thread over the top thread.This is achieved by the combined action of top thread tensioner 14 andstitch maker 15 which is driven by stitch maker motor 16 upwardly awayfrom graft 5 thereby closing the loop in the top thread. At the sametime, top thread tensioner 14 acts to tension the top thread so that thestitch maker 15 can pull against this tension to create the stitch.Similarly, shuttle thread tensioner 24 urges leaf spring 47 on shuttle40 so as to trap the bottom thread to prevent it from unspooling frombobbin 41.

Once the stitch is formed, shuttle drive arms 23 act in reverse to driveshuttle 40 backwards out of the lumen of graft 5 to make room for needle12 to drive again into graft 5 and form the next loop. The placement ofthe second stitch can be chosen so as to form a stitch over the supportwire, thereby stitching it to graft 5. This can be achieved by means ofneedle wobble drive 13 operating on needle 12 so as to achieve finepositioning of needle 12 with respect to the support wire and graft 5.

As the support wire is sewn to graft 5, the position of graft 5 withrespect to sew arm 10 is continually adjusted by means of the graftgrips, graft bed height drive 6 and graft tilt drive 8.

In an alternative embodiment, shuttle 50 is employed instead of shuttle40. Thread is wound onto bobbin 41 which is fitted into bobbin carrier51, and bobbin carrier 51 is seated in recess 54 in shuttle rod 53 asshown in FIG. 4C. Shuttle rod 53 is then moved back and forth in thesame manner described above for shuttle 40 in shuttle tube 20. Needle 12passes through slit 55 and then retracts slightly to form a loop.Shuttle rod 53 then advances further to engage nose 52 in said loop.Stitches are thereafter formed in the same way as above.

Although the invention has been defined in terms of applying thread to atubular medical implant, which can comprise a graft, a stent, agraft-stent, a graft fixation device, ophthalmic orbital reinforcementdevices, annuli for heart valve supports, vein implants, vein valvesupports or any other tubular medical form, it will be appreciated thatthe method and apparatus of the invention can equally be employed tostitch thread to the surface of any tubular form.

It will be appreciated that the parts of apparatus herein described maybe operated in order to achieve further objectives not specificallydescribed. For example, the apparatus may be used to form threedimensional textile structures such as artificial tissue structures orsubstrates to support the same.

1. A method for stitching thread to the wall of a tubular medicalimplant having a straight section with substantially parallel walls andat least one tapered section with tapered walls, the method comprisingthe steps of: a. driving a first thread through the wall and into thebore of the implant using a needle, b. forming a loop of the firstthread, c. moving a bobbin carrying a second thread through an open endof the implant into the bore, d. passing the second thread through theloop formed in the first thread, e. closing the loop in order to form astitch, and f. withdrawing the bobbin from the bore, wherein the implantis tilted in order that the axis along which the bobbin travels issubstantially parallel to the wall in which the stitch is to be formed.2. The method of claim 1 wherein the needle is provided on a mechanizedsewing machine.
 3. The method of claim 1 wherein the implant is atubular graft.
 4. The method of claim 1 wherein: a. the bobbin and theneedle are disposed so that the longitudinal axes thereof lie in acommon plane, and b. the needle is withdrawn sufficiently before thesecond thread is passed through the loop so that the bobbin and theneedle do not make contact.
 5. The method of claim 4 wherein: a. theloop is formed in the first thread by beginning to withdraw the needle,but b. the end of the needle is withdrawn completely from the bore onlyafter the bobbin has engaged the loop.
 6. A device for stitching threadto the surface of a tubular medical implant, comprising: a. a supportfor the implant, b. a needle to drive a first thread through the surfaceand into the bore of the implant, c. a bobbin for carrying a secondthread, d. means for moving the bobbin through an open end of theimplant into the bore in order to form a stitch in combination with thefirst thread, and d. means for tilting the implant relative to thedirection of movement of the implant.
 7. The device of claim 6additionally comprising means for determining the level of the implantsurface and controlling the height of the needle relative to the level.8. The device of claim 6 wherein the needle and the bobbin are disposedso that the longitudinal axes thereof lie in a common plane.
 9. Thedevice of claim 6 wherein an elongate bobbin support is provided tosupport the bobbin inside the bore of the implant.
 10. The device ofclaim 9 wherein the bobbin support is a rod having a recess in which thebobbin can be seated.
 11. The device of claim 9 wherein the bobbinsupport is a runner in which the bobbin is free to move into and out ofthe bore.
 12. The device of claim 11 in which the runner is in the formof a tube with a slot provided therein to allow the needle access to thebobbin through the slot.
 13. The device of claim 6 in which the bobbinsits in a shuttle.
 14. The device of claim 13 wherein the shuttle is anelongate element with a D-shaped cross section for at least part of itslength.
 15. The device of claim 6 additionally comprising means fortensioning the first thread, wherein the means for tensioning operatesindependently of the mechanism for driving the needle.
 16. A method forstitching thread to the wall of a tubular medical implant having astraight section with substantially parallel walls and at least onetapered section with tapered walls, the method comprising the steps of:a. driving a first thread through the wall of the straight section ofthe implant and into the bore of the implant using a needle, b. forminga loop of the first thread, c. moving a bobbin carrying a second threadthrough an open end of the implant into the bore, d. passing the secondthread through the loop formed in the first thread, e. closing the loopin order to form a stitch, f. withdrawing the bobbin from the bore, g.tilting the implant so that one of the walls of the tapered section ofthe implant is substantially parallel to the direction of movement ofthe bobbin, and h. repeating steps a to f in order to form a stitch inthe tapered wall.
 17. The method of claim 16 wherein steps a to f arecarried out several times followed by step g, and then step h is carriedout several times.
 18. The method of claim 16 wherein the needle isprovided on a mechanized sewing machine.
 19. The method of claim 16wherein: a. the bobbin and the needle are disposed so that thelongitudinal axes thereof lie in a common plane, and b. the needle iswithdrawn sufficiently before the second thread is passed through theloop so that the bobbin and the needle do not make contact.
 20. Themethod of claim 19 wherein: a. the loop is formed in the first thread bybeginning to withdraw the needle, but b. the end of the needle iswithdrawn completely from the bore only after the bobbin has engaged theloop.